This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. During the previous funding period, we have invested considerable effort and time in merging tetracysteine tags with other reporter systems to generate hybrids with enhanced performance for both LM and EM detection. This report covers the progress we made in: (1) Enhancing the sensitivity and the signal/noise ratio of protein detection with biarsenicals. (2) Detecting nucleic acids and interacting proteins in correlated LM/EM studies. (3) Developing a photo-reversible protein aggregation tag for functional studies. (4) Labeling with biarsenicals after fixation. (5) Developing methods for the simultaneous preservation of fluorescent signals, ultrastructure and antigenicity. (6) Developing multiple labeling strategies using EEL spectroscopy.